The system described in patent document 1 is known as a solar electric power generation system that works with external power source (system side power source) such as a commercial electric power system, etc.
The solar electric power generation system comprises: a solar battery module; an electric storage device; a discharge control device that controls the discharging of the electric storage device; a charge control device that controls the charging from external power source to the electric storage device; and an electric inverter that takes the electric power of the solar battery module or electric storage device as the input and supplies electric power to the external power source or electric loads; wherein, the solar battery module is connected to the electric inverter in a way that it inputs the electric power generated by it to the electric inverter, the electric storage device is connected to the electric inverter in a way that it inputs the electric power via the discharge control device to the electric inverter, and the electric storage device is connected to the external power source via the charge control device; when the electric inverter operates, the discharge control device controls the discharging of the electric storage device in a way that the electric power input from the solar battery module or electric storage device to the electric inverter is always maintained above a specified value.
In addition, in the solar electric power generation system, the electric inverter always operates with electric power input above the specified value, so that it always maintains a high inversion efficiency; moreover, the electric storage device is charged from the external power source under control of the charge control device, and therefore the charging is not affected by the output of the solar battery module and the electric quantity of charge can always be achieved as planned; hence, the phenomenon of inadequate charged electric quantity can be avoided.